EP0436577A1 - Procede et installation de mesure pour la determination de grandeurs mecaniques. - Google Patents

Procede et installation de mesure pour la determination de grandeurs mecaniques.

Info

Publication number
EP0436577A1
EP0436577A1 EP89910424A EP89910424A EP0436577A1 EP 0436577 A1 EP0436577 A1 EP 0436577A1 EP 89910424 A EP89910424 A EP 89910424A EP 89910424 A EP89910424 A EP 89910424A EP 0436577 A1 EP0436577 A1 EP 0436577A1
Authority
EP
European Patent Office
Prior art keywords
abutment
measuring device
measuring
servomotor
sensor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP89910424A
Other languages
German (de)
English (en)
Other versions
EP0436577B1 (fr
Inventor
Juergen Horn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Dr Hans Boekels & Co GmbH
Boekels & Co H
Original Assignee
Dr Hans Boekels & Co GmbH
Boekels & Co H
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Dr Hans Boekels & Co GmbH, Boekels & Co H filed Critical Dr Hans Boekels & Co GmbH
Publication of EP0436577A1 publication Critical patent/EP0436577A1/fr
Application granted granted Critical
Publication of EP0436577B1 publication Critical patent/EP0436577B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G23/00—Auxiliary devices for weighing apparatus
    • G01G23/06—Means for damping oscillations, e.g. of weigh beams
    • G01G23/10—Means for damping oscillations, e.g. of weigh beams by electric or magnetic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances

Definitions

  • the invention relates to a method for determining mechanical measured variables, in which a measured variable transducer elastically deforms under the action of the measured variable to be determined, thereby transforming the mechanical measured variable into a proportional electrical measurement signal, and in which the transducer abutment after a change in the measured variable or the action of a disturbance variable is forced to a sensibly controlled counter movement relative to the inertial system.
  • the invention further relates to a corresponding measuring device for determining mechanical measured variables with a transducer which deforms elastically under the action of a mechanical measured variable and which converts the measured variable into a proportional electrical signal, and with an electrically controllable servomotor which actuates the transducer abutment after a sudden change in the Measured variable or the action of a disturbance variable to meaningful counter movements relative to the inertial system.
  • Measuring devices for the determination of mechanical measurands such as forces, weights, torques, voltages, pressures or distances, often contain an elastic transducer which deforms elastically and proportionally to the measured variable to be determined.
  • Such transducers can be resistive, capacitive or inductive in nature, with the deformation or out steering of the measuring spring body then leads to the transformation of the mechanical measured variable into a - mostly proportional - electrical measuring signal. Due to its elastic deformation, the transducer stores a potential energy that has to be applied by the measurement object. As a rule, this is subject to mass and thus has, for example, an inert mass, an moment of inertia or an inertia.
  • this unit then forms an oscillatory system which, after a sudden change in the input variable, undergoes a settling process which is more or less long depending on the internal damping of the system, before it reaches its steady state of equilibrium comes to rest.
  • the period of the settling cycles is - not linear - proportional to the inertia and the flexibility of the elastic transducer.
  • critical damping up to which overshoots occur via the new stationary equilibrium position, the period of the natural oscillation increases in the same direction and the duration of the transient process shortens in the opposite direction with the natural damping of the measuring system. If this is greater than the critical damping, the system no longer swings beyond the stationary end position, but slowly approaches it asymptotically.
  • the new steady state of equilibrium and thus the corresponding parameter can be determined by intelligent evaluation of the first measured data after changing the measured variable Estimate the measured value.
  • the precalculated dynamic course of the transient process can be continuously compared with the actual sensed course, and the accuracy of the estimated measured value can thus be continuously increased until it lies within predetermined limits.
  • the use of such estimation methods requires intelligent electronics that are individually adapted to the respective measuring device and require a lot of software. Depending on the required accuracy, a usable measured value is available after a period of at least two periods of a weakly damped oscillating system.
  • the object of the present invention is to provide a method and a measuring device with which it is possible to greatly shorten the settling times of such measuring systems with elastic transducers.
  • this task is solved in that the transducer abutment is forced to perform a sensibly controlled counter movement relative to the inertial system (center of the earth) after a sudden change in the measured variable.
  • the task of describing a corresponding device is achieved in that an electrically controllable servomotor is provided which moves the abutment of the elastic measurement variable sensor after a change in the measured variable and in that the device outputs the output signal of the sensor processing circuit for controlling the servo motor comprises.
  • an electrically controllable servomotor is provided which moves the abutment of the elastic measurement variable sensor after a change in the measured variable and in that the device outputs the output signal of the sensor processing circuit for controlling the servo motor comprises.
  • it is sufficient for the oscillatory system if it has a low passive internal damping in order to achieve extremely short transient damping. This is made possible by the use of a servomotor which is controlled by the Output signal of the elastic transducer, which moves the transducer abutment after a change in the input variable in such a way that any vibration energy is withdrawn from the measuring system in the shortest possible time.
  • the servomotor succeeds in causing the transducer abutment to move in such a short time that the absolute size (amount) is the same, but exactly opposite in its respective direction to the displacements with which the load introduction point of a conventional, i.e. reacts to sudden changes in the measured quantity with an immobile sensor bearing.
  • the elastic energy to be stored in the steady state of equilibrium after the introduction of a measurement variable other than zero into the elastic sensor, the measuring spring, is therefore no longer applied by the test object itself, but by the servomotor. Since the measuring system then opposes the measured variable with an equally large reaction component at all times, it appears completely unyielding to the outside, i.e.
  • the servomotor can be controlled directly by the electrical output signal of the measuring spring, since this signal provides information about the instantaneous deflection of the elastic sensor without delay at any time. Deflection is understood to mean the relative movement between the load introduction point and the sensor abutment.
  • an actuator with limited output will naturally not be able to convert the mass-bearing transducer abutment to the deflection of the measuring spring in an infinitely short time after a change in the measured variable bring completely compensating counter-displacement and at the same time preload the measuring spring to the required extent.
  • the counter-displacement is carried out in such a way that it only leads to a time-delayed and / or only almost complete compensation of the deflection of the measuring spring.
  • the stiffness of the measuring system also appears to be significantly increased to the outside, the natural frequency of the measuring system and its natural damping increasing to the same extent.
  • the counter-displacement of the transducer abutment is therefore continued until the moment at which dynamic deflections of the measuring spring have completely subsided.
  • this is not absolutely necessary for the functioning of the system according to the invention. A single movement of the abutment against the deflection of the measuring spring leads to considerably reduced settling times.
  • a position sensor is therefore to be provided which detects the displacements of the transducer abutment and enables its position control.
  • the position control or regulation described above is therefore based on a system analysis of the transducer abutment replaced by a speed control.
  • the manipulated variable or command variable required to control the speed servomotor, the deflection speed of the transducer can be obtained in the simplest case by differentiating its electrical output signal.
  • the control of the servomotor for moving the transducer abutment is carried out by an intelligent circuit with a microcomputer.
  • the known, most important system parameters of the respective measuring device can be used for intelligent control or regulation of the abutment movement.
  • the optimal countermovement of the transducer abutment in terms of the shortest possible settling time can be calculated in advance from the time course of the first measured values detected by the transducer after a sudden change in the measured variable and can be carried out using the full drive power of the servomotor used.
  • the course of the counter movement calculated as the best possible can be continuously corrected and further optimized by scanning the sensor output signal influenced by this movement.
  • there is of course the high cost of intelligent control or regulation which can be justified in the case of exceptionally critical application cases.
  • the natural damping of a measuring device increases in proportion to the increase in the natural frequency. If the mass of the moving parts of the servomotor and the transducer abutment is small compared to the total mass composed of the masses of the test object and the moving parts on the load introduction side of the transducer, then it is made from a series with Damping device resulting in the servomotor lying likewise and increased to the same extent by the device according to the invention.
  • a mechanical, series-acting damping device makes little sense here, however, since it would still be fully loaded by the measured variable and all dead loads even after the measuring device had completely settled in and the servomotor would consequently have to constantly move the input of the damping device in order to calmly exit it hold.
  • Figure 1 shows the schematic structure of a strain gauge scale according to the invention with a servomotor, a control circuit, a displacement sensor and an electronic evaluation circuit.
  • FIG. 2 shows the block diagram of the arrangement according to FIG. 1, additionally equipped with a mechanical damping device acting parallel to the measuring spring;
  • Fig. 3 shows the transient response of an inventive
  • Measuring device compared to that of a not or only weakly damped, conventional elastic measuring system
  • FIG. 4 shows the block diagram of the arrangement according to FIG. 1, additionally provided with a mechanical damping device acting in series with the servomotor;
  • Fig. 5 shows the block diagram of the arrangement according to Fig. 1, wherein the mechanical damping device according to
  • Fig. 4 has been replaced by an electrical damping element.
  • the measuring transducer 1 shows the structure of a measuring device according to the invention using the example of an electromechanical elastic weighing device.
  • the measuring transducer 1 works here according to the strain gauge principle, in which the mechanical deformation of a spring body proportional to the deflection is caused by resistive, generally elements 6 arranged in a bridge circuit are converted into an electrical output signal. Without the elements shown in the upper area of FIG. 4, the position sensor 5, the control circuit 8 and the servomotor 9 with gear 4, this was a conventional strain gauge scale with a fixed, i.e. Compared to the inertial system of the stationary abutment S.
  • the output signal from the bridge circuit from the strain gauges 6 mounted on the measuring spring has changed from uo to a value by, is electrically amplified by the amplifier 7 and converted by the electronics 10 into a digital measured value displayed by the unit 11.
  • the weight 2 to be measured forms together with the dead load the weighing pan and moving parts of the measuring spring 1 in unity with the resilience of the spring an oscillatory system. For this reason, the new steady state of equilibrium of the measuring device will only set after a sudden, possibly impulsive change in the measured variable after a transient process which is more or less long depending on the natural damping of the arrangement. In the normal case, strain gauge measuring devices are extremely difficult to use due to their small spring deflections and are mechanically dampened with regard to the measuring accuracy.
  • the sensor abutment S is no longer stationary, but can be moved by the servomotor 9, possibly via a gear 4.
  • the control of the servomotor 9 is carried out by the amplifier element 8, the input variables of which are the output signal amplified by 7 around the transducer bridge and possibly the electrical output signal Ua of the position sensor 5 which detects the displacement Sa of the transducer abutment S.
  • the control of the abutment movement is designed in such a way that:
  • Sm (t) is zero at all times, ie the flexibility of the measuring system also appears to be zero.
  • a real servomotor with limited power can of course not change the position of a mass-loaded body by leaps and bounds, so that there will always be a time delay between the control variable by (t) and the deflection Sa (t) of the abutment S. Depending on the size of this delay, this can result in instability of the measuring device according to the invention.
  • the path control / regulation is replaced by a speed control / regulation.
  • the block diagram according to FIG. 2 shows such a system in which a servo motor VA acting as a speed actuator moves the transducer abutment S at a speed va, "mx" is the inert mass of the weighing sample, FE its weight, mo the inert mass of the moving dead load of the measuring system (load shell, etc.), and Fo is finally the weight of this dead load.
  • the switches T. and T2 are open until the measuring object is placed on the weighing pan, then closed, so that the weight force FE and the inertial mass mx then act on the measuring system.
  • N is the resilience of the elastic transducer, ms the inertial mass of the transducer abutment and the parts moving with it, e.g. of the servomotor.
  • a damping element Dp is arranged, which on the one hand includes the natural damping (e.g. air), and on the other hand possibly includes other artificial damping devices attached to the measuring system.
  • the control inputs of the control electronics A for the servomotor VA are acted upon by signals which correspond on the one hand to the speed va of the transducer abutment and on the other hand to the deflection speed vn of the measuring spring.
  • the difference between the two signals is amplified by the factor k, so that the servomotor in turn moves the abutment at the speed Va D.
  • this compensating measuring system equipped according to the invention like a conventional one, also reaches the new steady state of equilibrium via a damped, ie gradually decaying oscillation, but the deflection SN (t) B of the measuring spring has the following time profile: 4 So here the oscillations have a natural frequency foB and a damping factor DB, which have increased by a factor of (1 + k) 0.5 compared to the system without compensation with the parameters fo and Do. So the following applies:
  • FIG. 3 shows the transient response of a measuring device according to the invention compared to that of a weakly damped, conventional elastic measuring system.
  • the measuring spring of the system equipped according to the invention only executes vibrations with a period duration ToB reduced to To / 5, the rest of which is already less than 0.89% of is.
  • the measuring system behaves in the same way as the arrangement according to FIG. 2, if according to FIG. 4 the damping device Dp from FIG. 2 acting parallel to the measuring spring is replaced by a series-acting damper Ds.
  • the mechanical damping device Ds can be transformed into a simple ohmic resistance Rs according to FIG. 5 if the servomotor VA is designed such that UEM applies to its electromechanical transmission ratio:
  • a simple electrical component takes over, in the arrangement according to FIG. 5, the ohmic resistance Rs, which is otherwise often only partially or also completely mechanically implemented by a corresponding device Ds or DP.
  • a control unit (for VA)

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

Abstract

Une balance présentant un capteur élastique de grandeurs à mesurer, fonctionnant suivant le principe de la jauge extensométrique (DMS), comprend essentiellement un dynamomètre (1), un plateau porte-charge (3) pour l'introduction de la grandeur de mesure, ainsi qu'une unité d'évaluation et d'affichage (7, 10, 11) qui fournissent une valeur de mesure à partir du signal de sortie fourni par le DMS. On a prévu un servomoteur (9) réglable électriquement, muni, le cas échéant, d'un mécanisme de transmission (4), qui de la même façon, est commandé par le signal de sortie électrique du capteur (1), ainsi qu'éventuellement par le signal de sortie d'un détecteur de position (5) décrivant le déplacement de la butée (S) du capteur, et qui déplace ladite butée de façon appropriée, de telle manière que toute énergie d'oscillation soit supprimée, en un temps minimal, du dispositif de mesure. De cette façon, les phénomènes oscillatoires sont très brefs et on obtient des valeurs de mesure utilisables, d'une précision appropriée, en une fraction du temps requis pour un dispositif de mesure élastique conventionnel.
EP89910424A 1988-09-27 1989-09-25 Procede et installation de mesure pour la determination de grandeurs mecaniques Expired - Lifetime EP0436577B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3832751 1988-09-27
DE3832751A DE3832751A1 (de) 1988-09-27 1988-09-27 Verfahren und messeinrichtung zur bestimmung mechanischer messgroessen

Publications (2)

Publication Number Publication Date
EP0436577A1 true EP0436577A1 (fr) 1991-07-17
EP0436577B1 EP0436577B1 (fr) 1992-03-25

Family

ID=6363800

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89910424A Expired - Lifetime EP0436577B1 (fr) 1988-09-27 1989-09-25 Procede et installation de mesure pour la determination de grandeurs mecaniques

Country Status (3)

Country Link
EP (1) EP0436577B1 (fr)
DE (2) DE3832751A1 (fr)
WO (1) WO1990003555A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993005374A1 (fr) * 1991-08-31 1993-03-18 Kyoei Automatic Control Technology Co., Ltd. Procede et dispositif de mesure d'une charge dynamique

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1878554A (en) * 1927-02-11 1932-09-20 Dayton Scale Co Electrical scale
GB525165A (en) * 1939-02-16 1940-08-22 Harlan Albert Hadley Mechanism for limiting and checking the oscillations of the beam of a weighing scale
CH508204A (de) * 1970-06-18 1971-05-31 Mettler Instrumente Ag Electromagnetische Waage mit einer Vorrichtung zur Dämpfung von Pendelschwingungen
CH586897A5 (fr) * 1975-07-22 1977-04-15 Mettler Instrumente Ag

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9003555A1 *

Also Published As

Publication number Publication date
DE3832751A1 (de) 1990-05-10
EP0436577B1 (fr) 1992-03-25
DE58901052D1 (de) 1992-04-30
WO1990003555A1 (fr) 1990-04-05

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